The present invention relates to a portable electric power tool such as an electric router, and more particularly, to the portable electric router capable of performing chamfering and groove forming operations by rotating a rotary cutting bit fixed to a motor shaft.
The portable electric router is a tool for performing chamfering or grooving work on a workpiece made of, for example, wood. This is an especially indispensable tool for producing furniture. FIG. 7 shows an example of a conventional portable electric router. The electric router includes a base 311, a housing 312, an electric motor (not shown), and a chuck 317. The base 311 serves as a guide when sliding on a work-piece W such as a wood. The housing 312 is movably supported on the base 311. The motor is housed in the housing 312 and has a motor shaft, whose lower end is provided with the chuck 317 for mounting a cutting bit 318 which may take on various forms. The bit 318 is rotated by rotation of the motor and can therefore perform beveling or chamfering work and groove forming work with respect to the workpiece W.
This type of tool must be highly efficient at cutting, must be lightweight, and easy to maneuver, and capable of producing good finished surfaces. Of these basic capabilities, if the finishing level is sufficient to make a product, normally cutting efficiency is most demanded for improving production. Generally, increasing the lamination volume of an electric motor is a general method to enhance the cutting efficiency. This leads to enlargement of the motor size and increase in its rotation power. However, enlarging the size of the motor increases the overall weight of the tool, so does the cost of production. Resultant electric router does not provide sufficient transportability and operability or workability, those being other requisite factors.
U.S. Pat. No. 5,375,637 discloses a router having an improved cooling fan. As shown in FIG. 8, a motor 313 includes a stator 314 having a stator coil and a stator core, and an armature 315 having an armature coil and an armature core. A cooling fan 320 is mounted to the lower portion of an armature shaft 316, i.e.; the motor shaft. The cutting bit 318 is mounted onto the lower end of the armature shaft 316 by the, chuck 317. The cooling fan 320 is an improved axial-flow fan for improving cutting efficiency. To this effect, a ring 323 is provided to which each radially outer peripheral edge of a fan blade of the axial flow fan 320 is connected. Thus, inertial moment of the entire rotating components including the armature 315, the armature shaft 316, the cooling axial flow fan 320, the chuck 317, and the cutting bit 318 can be increased without enlargement of the motor 313.
However, the axial-flow fan 320 provides less cooling efficiency and increases noise if the axial-flow fan is used to permit the air to pass through a narrow passage for cooling the motor 313. Particularly, loud noise is generated even at the operation under no load.
A radial fan generates noise lesser than that released from the axial-flow fan. However, a fan guide must be provided between a discharge side of a fan blade and a motor in order to guide the flow of the cooling air and to prevent the cooling air from being discharged toward the motor side. This increased in numbers of components, and lowers assembleability to increase a production cost.